Abstract

A new adaptive optics system for the eye using a pyramid wavefront sensor interfaced in closed-loop with a piezoelectric deformable mirror is presented. Sensing parameters such as CCD integration time, pupil sampling and beam steering amplitude are tested on the bench and in vivo on several volunteers to optimize real-time optical correction. The system allows closed-loop operation at a frame rate of 55 Hz and reduces ocular aberration up to λ/5 residual RMS over a 6 mm pupil. Aberration correction and mirror control stability clearly increase when smaller beam steering amplitudes synonymous of higher wavefront sensing sensitivity are used. This result suggests that using pyramid wavefront sensors can improve the performance of adaptive-optics system for ophthalmic applications.

RMS values of the reconstructed OPD map for a range of commands applied to the central actuator, while all other actuator are set at the bias position. The upper and lower curves correspond to RMS values obtained when sensing the wavefront with modulations of 28 and 7 λ/D, respectively, showing a clear reduction in RMS error for the lower modulation case

Left: Time evolution of the optical path difference RMS as recorded on a volunteer while closing the adaptive loop (7 λ/D modulation). Each spike corresponds to an eye blink. Center: Enlarged sequence showing the onset of the closed-loop correction. Right: maps of the wrapped phase before (up) and during (down) closed-loop operation

Left: Residual optical path difference RMS achieved during closed-loop correction for different modulation amplitude. Right: Average variance on the command corrections sent to the mirror for the same range of modulation amplitudes